Optimized lid attach process for thermal management and multi-surface compliant heat removal

ABSTRACT

A multi-surface compliant heat removal process that includes identifying components to share a heat rejecting device; applying non-adhesive film to the components; identifying a primary component of the components; and applying phase change material on each of the components, other than the primary component. The phase change material is placed on top of the non-adhesive film. The process also includes placing the heat rejecting device on the corresponding components and removing the heat rejecting device from the corresponding components. The phase change material and the non-adhesive film remain with the heat rejecting device. The process also includes reflowing the phase change material on the heat rejecting device; removing the non-adhesive film from the heat rejecting device; placing a heatsink-attach thermal interface material on the components; and placing the heat rejecting device on the corresponding components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/121,337 filed May 15, 2008, now U.S. Pat. No. 7,939,364.

BACKGROUND OF INVENTION

The assembly of a semiconductor package plays an important role inthermal management. A conventional semiconductor package includes a lid,one or more die, a die interconnect, a substrate, a substrateinterconnect, and lid-attach thermal interface material (“TIM”).

The die is placed on the substrate through a die-attach process.Typically, the die-attach process involves attaching a flip-chip typedie to the substrate by the die interconnect through a reflow process.The underfill is applied to the die interconnect, the die, and thesubstrate. The lid-attach TIM is applied to the bottom side of the die(the side opposite the die interconnect). The lid is placed on thesubstrate, typically making contact with the die by way of thelid-attach TIM. The semiconductor package is cured at a curingtemperature. The bond line thickness (“BLT”) of the lid-attach TIM isdetermined by the co-planarity of the die, substrate, and lid, theapplication of the lid to the substrate, the characteristics of thelid-attach TIM, and the curing process of the assembled semiconductorpackage.

Conventional techniques for heat removal from a microprocessor,application specific integrated circuit (“ASIC”), integrated circuit(“IC”), or other printed circuit board (“PCB”) component rely upon theuse of the heatsink-attach TIM placed between the heat generating deviceand a heat rejecting device. Typically, a single heat rejecting device,i.e., a heatsink, spans several components on the heat generatingdevice, i.e., a semiconductor package. The BLT of the heatsink-attachTIM determines the thermal path performance and cooling efficiency ofthe heat rejecting device.

SUMMARY OF INVENTION

According to one aspect of one or more embodiments of the presentinvention, a semiconductor package assembly process comprising:attaching one or more die to a substrate by a die-attach interconnect;raising a temperature of the one or more die to a target temperature;placing a lid-attach thermal interface material on the one or more dieupon reaching the target temperature; placing a lid on the substrate toachieve a target bond line thickness of the lid-attach thermal interfacematerial between the one or more die and the lid; and curing theassembled semiconductor package at a curing temperature.

According to one aspect of one or more embodiments of the presentinvention, a multi-surface compliant heat removal process comprising:identifying one or more components to share a heat rejecting device;applying a non-adhesive film to the one or more components; identifyinga primary component of the one or more components; applying a phasechange material on each of the one or more components other than theprimary component, wherein the phase change material is placed on top ofthe non-adhesive film; placing the heat rejecting device on thecorresponding one or more components; removing the heat rejecting devicefrom the corresponding one or more components, wherein the phase changematerial and the non-adhesive film remain with the heat rejectingdevice; reflowing the phase change material on the heat rejectingdevice; removing the non-adhesive film from the heat rejecting device;placing a heatsink-attach thermal interface material on the one or morecomponents; placing the heat rejecting device on the corresponding oneor more components.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process for assembling a semiconductor package in accordancewith one or more embodiments of the present invention.

FIG. 2( a) is a warped flip-chip die that is die-attached to a substrateby a die-attach interconnect after a reflow process in accordance withone or more embodiments of the present invention.

FIG. 2( b) is the flattened out flip-chip die with lid-attach TIMapplied, the die is die-attached to the substrate and raised to anelevated temperature in accordance with one or more embodiments of thepresent invention.

FIG. 2( c) is an assembled semiconductor package in accordance with oneor more embodiments of the present invention.

FIG. 3 is a process for implementing multi-surface compliant heatremoval in accordance with one or more embodiments of the presentinvention.

FIG. 4( a) is a substrate with a primary component, a secondarycomponent, and non-adhesive film placed on the primary and secondarycomponent in accordance with one or more embodiments of the presentinvention.

FIG. 4( b) is the substrate with the primary component, secondarycomponent, non-adhesive film, PCM, and placed heat rejecting device inaccordance with one or more embodiments of the present invention.

FIG. 4( c) is the substrate with the primary component and secondarycomponent, and removed heat rejecting device, PCM, and non-adhesive filmin accordance with one or more embodiments of the present invention.

FIG. 4( d) is the substrate with the primary component, secondarycomponent, and heatsink attach-TIM, and removed heat rejecting deviceand reflowed PCM in accordance with one or more embodiments of thepresent invention.

FIG. 4( e) is the substrate, primary component, secondary component,reflowed PCM, re-placed heat rejecting device, and heatsink-attach TIMin accordance with one or more embodiments of the present invention.

DETAILED DESCRIPTION

Specific embodiments of the present invention will now be described indetail with reference to the accompanying figures. Like elements in thevarious figures are denoted by like reference numerals for consistency.Further, in the following detailed description of embodiments of thepresent invention, numerous specific details are set forth in order toprovide a more thorough understanding of the present invention. In otherinstances, well-known features have not been described in detail toavoid obscuring the description of embodiments of the present invention.

FIG. 1 shows a process for assembling a semiconductor package inaccordance with one or more embodiments of the present invention. In S1,a flip-chip die is die-attached to a substrate by a die-attachinterconnect through a reflow process. The die-attach interconnect couldbe a Controlled Collapse Chip Connection, also known as C4, or otherdie-attach interconnect. One of ordinary skill in the art will recognizethat other die-attach interconnects could be used in accordance with oneor more embodiments of the present invention. The die and substrate maydiffer in construction or materials. The die and substrate may differ intheir respective coefficient of thermal expansion. The die and substratemay, individually or collectively, exhibit warpage prior to, during, orafter the reflow process.

In S2, an underfill material is flooded between the die, the substrate,and the die-attach interconnect. The underfill may be cured separatelyor concurrently with the lid-attach TIM, depending on the curingtemperature profile. In S3, the die-attached substrate is raised to anelevated temperature in a controlled manner. The elevated temperaturemay be 150 degrees C. or any other temperature in which the die becomesflat or more nearly flat. The elevated temperature may be the curingtemperature for the lid-attach TIM. In S4, the lid-attach TIM is placedon the bottom side of the die or the corresponding side of a lid. In S5,the die-attached substrate and lid are pressed together to achieve thedesired BLT of the lid-attach TIM. In S6, the assembled semiconductorpackage is cured at a curing temperate. The curing temperature may bethe same temperature utilized in S3 or a different temperature.

FIG. 2( a) shows a warped flip-chip die 105 that is die-attached to asubstrate 110 by a die-attach interconnect 115 after a reflow process inaccordance with one or more embodiments of the present invention. Anunderfill 120 is flooded between the die 105, the substrate 110, and thedie-attach interconnect 115. The die 105 and substrate 110 may differ inconstruction and materials. The die 105 and substrate 110 may differ intheir respective coefficient of thermal expansion. The die 105 andsubstrate 110 may, individually or collectively, exhibit warpage priorto, during, or after the reflow process. The temperature of thedie-attached substrate 110 may be raised to an elevated temperature in acontrolled manner. The elevated temperature may be 150 degrees C. or anyother temperature in which the die 105 becomes flat or more nearly flat.

FIG. 2( b) shows the flattened out flip-chip die 105 with lid-attach TIM125 applied, the die 105 is die-attached to the substrate 110 and raisedto an elevated temperature in accordance with one or more embodiments ofthe present invention. The die 105 may become flat or more nearly flatas a result of being raised to an elevated temperature.

FIG. 2( c) shows an assembled semiconductor package in accordance withone or more embodiments of the present invention. The flattened outflip-chip die 105 is die-attached to the substrate 110 by dieinterconnect 115 through the reflow process. The underfill 120 isflooded between the die 105, the substrate 110, and the die-attachinterconnect 115. A lid-attach TIM 125 may be placed directly on thebottom side of the die 105 or the corresponding side of a lid 130. Thedie-attached substrate 110 and the lid 130 may be pressed together toachieve a desired BLT of the lid-attach TIM 125. One of ordinary skillin the art will recognize that the BLT impacts the thermal resistance ofthe associated interface and the junction temperature when placed insystem.

FIG. 3 shows a process for implementing multi-surfaces compliant heatremoval in accordance with one or more embodiments of the presentinvention. In T1, a non-adhesive film is placed on all components thatare intended to be cooled by a single heat rejecting device. In T2, aphase change material (“PCM”) is placed on each component other than themost thermally demanding component. In T3, a heat rejecting device isplaced on the corresponding components in the appropriate locations byway of the PCM or non-adhesive film and the PCM is reflowed in place. InT4, the heat rejecting device is removed from the correspondingcomponents such that the heat rejecting device is attached to the PCMand the non-adhesive film. In T5, the non-adhesive film is removed fromthe heat rejecting device. In T6, the heatsink-attach TIM is placed onthe corresponding components. In T7, the heat rejecting device is placedon the corresponding components in the appropriate locations andattached.

FIG. 4( a) shows a substrate 405 with a primary component 410, asecondary component 415, and non-adhesive film 420 in accordance withone or more embodiments of the present invention. Substrate 405 may bethe substrate of a semiconductor package or a PCB. The primary component410 and secondary component 415 may differ in height, shape, size, orconstruction. A non-adhesive film 420 is placed on the primary component410 and the secondary component 415.

FIG. 4( b) shows the substrate 405, primary component 410, secondarycomponent 415, non-adhesive film 420, PCM 425, and placed heat rejectingdevice 430 in accordance with one or more embodiments of the presentinvention. The primary component 410 is the most thermally demandingcomponent. Accordingly, PCM 425 is placed on the secondary component415. The heat rejecting device 430 is placed making contact with theprimary component 410 by way of non-adhesive film 420 and making contactwith the secondary component 415 by way of the PCM 425 and non-adhesivefilm 420. The PCM 425 is reflowed in place.

FIG. 4( c) shows the substrate 405 with the primary component 410 andsecondary component 415, and removed heat rejecting device 430, PCM 425,and non-adhesive film 420 in accordance with one or more embodiments ofthe present invention. Heat rejecting device 430 is removed from theprimary component 410 and secondary component 415 such that the heatrejecting device 430 now contains the PCM 425 and non-adhesive film 420.

FIG. 4( d) is the substrate 405 with the primary component 410,secondary component 415, and heatsink attach-TIM 435, and removed heatrejecting device 430 and reflowed PCM 425 in accordance with one or moreembodiments of the present invention. The non-adhesive film 420 isremoved from the heat rejecting device 430 leaving the reflowed PCM 425in place. Heatsink-attach TIM 435 is placed on the primary component 410and the secondary component 415.

FIG. 4( e) shows the substrate 405, primary component 410, secondarycomponent 415, reflowed PCM 425, re-placed heat rejecting device 430,and heatsink-attach TIM 435 in accordance with one or more embodimentsof the present invention. The heat rejecting device 430 is placed on theprimary component 410 and the secondary component 415 by way of theheatsink-attach TIM 435 and is attached. One of ordinary skill in theart will recognize that there are a variety of ways in which the heatrejecting device 430 may be attached to the substrate 405 in accordancewith one or more embodiments of the present invention.

One of ordinary skill in the art will recognize that the presentinvention contemplates other configurations of components, semiconductorpackages, and PCBs in accordance with one or more embodiments of thepresent invention.

Advantages of one or more embodiments of the present invention mayinclude one or more of the following.

In one or more embodiments of the present invention, the semiconductorpackage assembly process results in a die that is flat or more nearlyflat that eliminates or minimizes the void between the die, lid-attachTIM, and lid.

In one or more embodiments of the present invention, the semiconductorpackage assembly process results in a more controlled BLT of thelid-attach TIM.

In one or more embodiments of the present invention, the semiconductorpackage assembly process results in a decrease in the thermal resistanceand lowers the junction temperature.

In one or more embodiments of the present invention, the multi-surfacecompliant heat removal process allows for the placement of a single heatrejecting device that spans a plurality of components.

In one or more embodiments of the present invention, the multi-surfacecompliant heat removal process accommodates components that vary inheight due to design, assembly, or tolerance.

In one or more embodiments of the present invention, the multi-surfacecompliant heat removal process results in a more controlled BLT of theheatsink-attach TIM for all components under a single heat rejectingdevice.

In one or more embodiments of the present invention, the multi-surfacecompliant heat removal process results in a decrease in the thermalresistance and lowers the junction temperature for all components undera single heat rejecting device.

In one or more embodiments of the present invention, the multi-surfacecompliant heat removal process allows for design simplification, such assmaller and cost-reduced heat rejecting device implementations.

In one or more embodiments of the present invention, the multi-surfacecompliant heat removal process allows for lower fan speeds in systemsutilizing heat rejecting devices with active cooling.

In one or more embodiments of the present invention, the multi-surfacecompliant heat removal process allows for reduced power consumption forsystem cooling.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having the benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A multi-surface compliant heat removal process comprising:identifying one or more components to share a heat rejecting device;applying a non-adhesive film to the one or more components; identifyinga primary component of the one or more components; applying a phasechange material on each of the one or more components other than theprimary component, wherein the phase change material is placed on top ofthe non-adhesive film; placing the heat rejecting device on thecorresponding one or more components; reflowing the phase changematerial on the heat rejecting device; removing the heat rejectingdevice from the corresponding one or more components, wherein the phasechange material and the non-adhesive film remain with the heat rejectingdevice; removing the non-adhesive film from the heat rejecting device;placing a heatsink-attach thermal interface material on the one or morecomponents; and placing the heat rejecting device on the correspondingone or more components.
 2. The multi-surface compliant heat removalprocess of claim 1, further comprising: attaching the heat rejectingdevice to a substrate.
 3. The multi-surface compliant heat removalprocess of claim 1, wherein the heat rejecting device is a singlecontiguous device that spans the one or more components.
 4. Themulti-surface compliant heat removal process of claim 1, wherein the oneor more components vary in at least one of height, shape, size, orconstruction.
 5. The multi-surface compliant heat removal process ofclaim 1, wherein the primary component has a greater thermal demand thanall other components of the one or more components.
 6. The multi-surfacecompliant heat removal process of claim 1, wherein a target bond linethickness of the heatsink-attach thermal interface material iscontrolled by compression of the one or more components and the heatrejecting device.